Rotating-anode x-ray tube with multiple focal areas

ABSTRACT

A rotating-anode X-ray tube wherein the anode target has a first focal plane made of tungsten and a second focal plane made of molybdenum, rhodium, silver or palladium, there are disposed opposite to said first and second focal planes first and second cathodes in such a manner that each cathode impinges electrons on the corresponding focal plane, the voltage to be impressed on these cathodes can be varied by an external means, and there can be obtained, as required, a hard X-ray from the first focal plane or a soft X-ray from the second focal plane.

United States Patent Inventors Yoshltaka Seki;

Kaname Tanabe, both of Yokohama-shi, Japan Appl. No. 786,22 1

Filed Dec. 23, 1968 Patented Oct. 5, 1971 Assignee Tokyo ShibauraElectric Co., Ltd.

Kawasaki, Japan Priority Dec. 28, 1967 Japan 42/84998 ROTATING-ANODEX-RAY TUBE WITH MULTIPLE FOCAL AREAS 9 Claims, 7 Drawing Figs.

U.S. Cl 313/56, 250/95, 313/60, 313/330 Int. Cl ..ll0lj 35/10, l-l05g1/34 Field of Search 313/55, 56, 60, 330; 250/90, 93, 94, 95, 99

[56] References Cited UNITED STATES PATENTS 2,298,335 10/1942 Atlee313/60 2,942,126 6/1960 Silbermann 313/56 3,113,233 12/1963 Kasten etal.. 313/60 3,328,626 6/1967 Natter et al 313/330 Primary Examiner-JohnKominski Assistant Examiner-E. R. LaRoche Attorney-George B. OujevolkABSTRACT: A rotating-anode X-ray tube wherein the anode target has afirst focal plane made of tungsten and a second focal plane made ofmolybdenum, rhodium, silver or palladium, there are disposed opposite tosaid first and second focal planes first and second cathodes in such amanner that each cathode impinges electrons on the corresponding focalplane, the voltage to be impressed on these cathodes can be varied by anexternal means, and there can be obtained, as required, a hard X-rayfrom the first focal plane or a soft X-ray from the second focal plane.

PATENTEI] HST SIB?! 3,610,984

BY W

ROTATlNG-ANODE X-RAY TUBE WITH MULTIPLE FOCAL AREAS The presentinvention relates to a rotating-anode X-ray tube.

Heretofore, the anode target of a rotating-anode X-ray tube chiefly usedin an X-ray apparatus for medical examination has consisted of acircular disk made of tungsten or an alloy mainly composed thereof.

As is well known, the X-rays emitted from an X-ray tube provided with atungsten target display a specific wave length distribution defined by acombination of the continuous X-ray whose wave length-intensitycharacteristic depends on the voltage impressed across the cathode andtarget of an X-ray tube and X-ray such as WLa, WLB, WKa, WKB,characteristic of the tungsten. The intensity of the X-rays issubstantially proportionate to the X-ray tube current.

Where ordinary X-ray photographs are taken for medical examination,there are practiced various methods, for example, of selecting an X-raytube voltage adapted for the object intended so as to obtain X--rays ofthe desired intensity or rendering the quality of X-rays hard using afilter made of aluminum or the like, with the view of generating X-rayshaving such wave length distribution as will display the best effectdepending on the parts of a foreground subject or thicknesses thereof tobe exposed to X-rays or the objects of taking such photographs.

With respect to the various parts of the human body such as thecirculatory system including the limbs, head, dental section, chest,heart, etc. and the digestive system which have heretofore constitutedthe general subjects of the X-ray photography, the object of suchphotography has been fully attained by means of an X-ray tube having theaforesaid tungsten target and by selecting proper photographingconditions.

However, the photography or what is called mammography of the softtissues of the breast intended for medical examination of the diseasesassociated with the mammary glands which have recently been taken up inradiology requires even the slightest differences in the density of thesoft tissues of the foreground subject to be distinctly indicated on anX-ray photograph. Since it is necessary to this end to provide a sourceof soft X-rays of great intensity, there have heretofore been used theX-rays generated by impressing a voltage having a peak value of to 50kvp. on an X-ray tube provided with a target made of tungsten or alloysthereof. However, the quality of X-rays generated by the conventionalX-ray tube at a peak voltage of 20 to 50 kvp. was not always suitable tophotograph the aforementioned soft tissues. The reason was that thecharacteristic X-rays obtained at said peak voltage only consisted ofvery long waves exceeding 1.4 Angstrom units mainly including Wu: andWLB. The X-rays of such wave lengths were useless for the desired X--rayphotography. On the other hand, the continuous X-ray had a certainsmooth wave length distribution, and naturally restricted the parts of aforeground subject which would be effectively photographed thereby, sothat this type of X-ray was, of course, unsuitable for the desiredphotography.

Exactly to record minute differences in the X-ray absorption by theforeground subject on an X-ray photographic film, there have heretoforebeen made various attempts, for example, of using an X-ray tube providedwith a tungsten target at a voltage selected from the peak range of from20 to 50 kvp. or constructing the X-ray irradiating window so as toobtain X- rays having a wave length distribution containing a great dealof a useful component for the desired photography. However, all theseattempts have not achieved fully satisfactory results.

The present invention provides a rotating-anode X-ray tube whichcomprises an anode target whose first focal plane consists of tungstenor an alloy mainly consisting thereof and emits hard X-rays and whosesecond focal plane consists of molybdenum, rhodium, silver, palladium oran alloy mainly consisting of any one thereof and, if required, emitssoft X- rays of great intensity, and at least one cathode so positionedas to-face either of these focal planes, and wherein the first andsecond focal planes are differentiated in use as occasion demands,making it possible not only to emit optimum X-rays for general purposeradiography but also to take distinct mammographic pictures.

The present invention can be more fully understood from the followingdetailed description when taken in connection with the accompanyingdrawing, in which:

FIG. 1 represents a rotating anode X-ray tube according to an embodimentof the present invention with a part indicated in section;

FIG. 2 is a diagram of an external circuit for supplying the X-ray tubeof FIG. 1 with the required current and voltage; and

FIGS. 3 to 7 show the sectional views of modified targets of the presentrotating-anode X-ray tube.

We have studied various materials for use as a target in the emission ofsoft X-rays in search for a suitable one and found that metals such asmolybdenum, rhodium, silver, palladium and alloys mainly consisting ofany one thereof are well adapted for use as a target in generating softX-rays.

Comparison of the radiation Dose and qualitites of X-rays emitted fromthe molybdenum and tungsten targets is given in Tables 1 and 2 below.

As shown in Table l, the molybdenum target emits a larger absoluteradiation quantity of X-rays than the tungsten target and the ratios ofemissions by these targets progressively increase until the tube voltagerises to 50 kvp.

With respect to the quality of X-rays irradiated, the molybdenum targetdisplays a larger half value layer of aluminum than the tungsten targetwithin the peak voltage of from 20 to 50 kvp. as shown in Table 2, andunder the same X-ray tube load, is more prominently abundant in usefulenergy range of X-rays Accordingly, the molybdenum target generatesXrays of great intensity in the wavelength zone around the energy of 20kv. which is most suitable for the soft X-ray radiography. and onlyslightly suffers the attenuation of X-ray intensity caused by means forcorrecting the wave length distribution such as filtration. Also atarget made of rhodium, silver, palladium, their alloys with molybdenumor alloys mainly consisting of at least one of these single metalsproduces useful X- rays having an enough intensity in the wave lengthzone around the energy of 20 to 26 kv. which is available for thedesired soft X-ray radiography at a tube voltage of 20 to 50 kvp.

As previously described, however, a target made of the above-listedmetals or alloys thereof is unsuitable for use at a tube voltageexceeding kvp., so that it is only available for the soft X-rayradiography and barred from application in general purpose Xrayradiography.

The X-ray tube of the present invention comprises a plurality ofindependently operable cathodes or at least' one cathode capable ofemitting electrons at varying positions and a target disposed oppositeto said cathode or cathodes whose focal plane corresponding to at leastone of these cathodes or at least one of the varying X-ray emittingpositions is made of tungsten or an alloy mainly consisting thereof andwhose focal plane corresponding to at least one of the remainingcathodes or at least one of the other X-ray emitting positions consistsof molybdenum, rhodium, silver, palladium or an alloy mainly consistingof any one thereof. Accordingly, the X-ray tube of the present inventionis freely applicable either in the soft X- ray or general purposeradiography by selectively exciting one of the plurality of cathodes orshifting the position of at least one cathode.

There will now be described an embodiment of the present invention byreference to the appended drawing. In FIG. 1, there is rotatablysupported a rotating anode section 3 by means of bearing on a stationarysection 2 sealed to one end of an evacuated envelope 1, said anodesection 3 being rotated by a coil 4 disposed on the outside. To thefurthest end of the terminal axle section 3a of the rotating anodesection 3 is fitted a circular umbrella-shaped target plate 5 whoseupper surface excluding the central part gently inclines downward.

To the other end of the evacuated envelope 1 is fixed a cathode means 8provided with two filaments 6 and 7 which are spatially arrangedopposite to the target plate 5 and are each independently operable bymeans of an external circuit as shown in FIG. 2. The target plate 5 andfilaments 6 and 7 are disposed in such relationship that the electronbeams 9 and 10 emitted from said filaments 6 and 7 are concentrated ontwo focal points 11 and 12 spatially located in the radial direction onthe inclined upper surface of the target plate 5. Where the target plate5 rotates, the loci of the two focal points 11 and 12 define twoconcentric circles of different radii on the surface of the target plate5.

According to this embodiment, the focal plane near the axial centerincluding the inner focal point 12 on the surface of the target plate 5consists of a circular disk 13 of tungsten and the outer focal planeincluding the outer focal point 11 is composed of a plate 14 ofmolybdenum which constitutes the base body of the target plate 5.

FIG. 2 represents an external circuit for supplying the X-ray tube withthe prescribed tube current and voltage. This circuit supplies a highvoltage by a high tension transformer across a plate 3 and therespective ends of the filaments 6 and 7. There is introduced anelectric current by a filament transformer 21 positioned between theterminals of the filaments 6 and 7. There may be contemplated variousmeans for supplying an electric current to either of the filaments 6 and7 as occasion demands. However, the illustrated circuit uses a changeswitch 22. It will be apparent that other types of external circuitsgenerally used in the X-ray tube may also be available if only saidfilaments are made interchangeably usable by various known means.

There will now be described various modifications of the target plate 5used in the aforesaid embodiment. The target of FIG. 3 has a base bodycomposed of molybdenum and constituting the inner focal plane. The outerplane consists of an annular plate of tungsten embedded in said basebody. The target of FIG. 4 has a base body made of molybdenum andconstituting the outer focal plane, and the inner focal plane, made oftungsten is embedded in said base body. It is also possible to fabricatethe targets of FIGS. 3 and 4 by preparing a base body constituting onefocal plane from tungsten and the other focal plane from molybdenum,rhodium, silver, palladium or an alloy mainly consisting of any onethereof. The relationship between the tungsten and other metals used inthe target in terms of their respective requirements and positions isdetermined by the object of using an X-ray tube, namely, according towhether the tube is demanded to emit large amounts of soft X-rays orhard X-rays.

In the targets of FIGS. 5 and 6 the first and second focal planes havedifferent angles of inclination so as to cause X- rays to be emittedinto different fields from these focal planes. In the target of FIG. 5the focal plane forming the base body has a smaller inclination than theother focal plane, and FIG. 6 represents a reverse arrangement. In bothcases, the base body may consist of either tungsten or molybdenum.

The target of FIG. 7 as a whole has a dish shape with a cavity formed inthe upper part. As illustrated, this target is fitted to an X-ray tubein inclined relationship thereby to reduce the space between the targetand foreground subject and minimize loss of X-rays therebetween.

As mentioned above, the X-ray tube of the present invention causes thefilaments of a cathode to be independently operated, namely, excites oneof the filaments to emit X-rays from the focal point of one focal planeconsisting of molybdenum for use in mammography and actuates the otherfilaments to release X-rays from the focal point of the other focalplane made of tungsten for use in the general photography of parts ofthe human body. Namely, the present invention makes it possibleselectively to carry out either the soft X-ray or general purposeradiography as occasion demands, using a single X-ray tube. Moreover,the present X-ray tube has a soft X-ray focal plane made of molybdenum,rhodium, silver, palladium or an alloy mainly consisting of any onethereof, so that there are always obtained suitable soft X-rays formammogra hy.

The foregoing embodiment relates to the case where there were used twocathodes having the same focal lengths. However, it is also possible tocause these cathodes to have different focal lengths, or to providethree or more cathodes.

If the X-ray irradiating window of the evacuated envelope is made ofberyllium it will be advantageous for the soft Xray radiography. Or ifthe envelope consists of glass, the fabrication of said window withthinner walls than the other parts of the envelope will offerconvenience.

What is claimed is:

1. A rotating anode X-ray tube with multiple focal areas for emittingoptimum X-rays for general purpose radiography and soft X-rays formammography, comprising:

a. an evacuated envelope, X-rays b. a rotatable anode means housed insaid envelope and provided with a target,

c. first and second concentric annular focal areas provided on saidtarget, said first focal area made of a metal selected from the groupconsisting of tungsten and an alloy consisting mainly of tungsten andsaid second focal area made of a metal selected from the groupconsisting of molybdenum, rhodium, silver, palladium and alloysconsisting mainly of any one thereof, and

d. a cathode means spaced from said target, and having two filamentseach of which is arranged opposite to each of said focal areas and isindependently operable by means of an external circuit.

2. An X-ray tube according to claim 1 wherein the upper peripheralportion of the target gently inclines outward and the focal planes aredisposed on said peripheral portion.

3. An X-ray tube according to claim 2 wherein the upper peripheralportion of the target inclines in two steps and the inner inclination issharper than the outer one.

4. An X-ray tube according to claim 2 wherein the upper peripheralportion of the target inclines in two steps and the inner inclination ismore gentle than the outer one.

5. An X-ray tube according to claim 2, 3 or 4 wherein the inner focalplane consists of tungsten and the outer focal plane of molybdenum.

6. An X-ray tube according to claim 2, 3 or 4 wherein the inner focalplane consists of molybdenum and the outer focal plane of tungsten.

7. An X-ray tube according to claim 2 wherein the upper peripheralportion of the target inclines upward toward the periphery and the focalplanes are disposed on said peripheral portion.

8. An X-ray tube according to claim 2 wherein the cathode membercomprises two filaments provided at different positions, and as occasiondemands, only either one thereof is operated by an external circuit.

9. A rotating-anode X-ray tube, comprising in combination:

a. a rotating anode section (3) sealed towards one end of an evacuatedenvelope (I) mounted on a stationary section (2) with electromagnetmeans (4) outside said envelope to rotate said anode section;

b. cathode means (8) at the other end of said evacuated envelope withspatially arranged inner and outer filaments (6 and 7) operable by meansof an external circuit; and,

c. a circular target plate (5) with an inclined surface mounted on saidanode opposite said cathode means (8) so that beams from said filaments(6 and 7) are concentrated on two focal points spatially separated inthe radial direction, this rotation of said target plate (5) definingtwo concentric circles of different radii by said two focal points,forming an inner focal plane near the axial center including the innerfocal point on the target plates consisting of a disc (13) made of afirst metal and an outer focal plane including the outer focal pointconsisting of a plate (14), made of a second metal, one of said metalsbeing mainly tungsten or an alloy mainly of tungsten while the other ofsaid metal is a metal selected from the group consisting of molybdenum,rhodium, silver, palladium or an alloy mainly of any one thereof.

2. An X-ray tube according to claim 1 wherein the upper peripheralportion of the target gently inclines outward and the focal planes aredisposed on said peripheral portion.
 3. An X-ray tube according to claim2 wherein the upper peripheral portion of the target inclines in twosteps and the inner inclination is sharper than the outer one.
 4. AnX-ray tube according to claim 2 wherein the upper peripheral portion ofthe target inclines in two steps and the inner inclination is moregentle than the outer one.
 5. An X-ray tube according to claim 2, 3 or 4wherein the inner focal plane consists of tungsten and the outer focalplane of molybdenum.
 6. An X-ray tube according to claim 2, 3 or 4wherein the inner focal plane consists of molybdenum and the outer focalplane of tungsten.
 7. An X-ray tube according to claim 2 wherein theupper peripheral portion of the target inclines upward toward theperiphery and the focal planes are disposed on said peripheral portion.8. An X-ray tube according to claim 2 wherein the cathode membercomprises two filaments provided at different positions, and as occasiondemands, only either one thereof is operated by an external circuit. 9.A rotating-anode X-ray tube, comprising in combination: a. a rotatinganode section (3) sealed towards one end of an evacuated envelope (1)mounted on a stationary section (2) with electromagnet means (4) outsidesaid envelope to rotate said anode section; b. cathode means (8) at theother end of said evacuated envelope with spatially arranged inner andouter filaments (6 and 7) operable by means of an external circuit; and,c. a circular target plate (5) with an inclined surface mounted on saidanode opposite said cathode means (8) so that beams from said filaments(6 and 7) are concentrated on two focal points spatially separated inthe radial direction, this rotation of said target plate (5) definingtwo concentric circles of different radii by said two focal points,forming an inner focal plane near the axial center including the innerfocal point on the target plates consisting of a disc (13) made of afirst metal and an outer focal plane including the outer focal pointconsisting of a plate (14), made of a second metal, one of said metalsbeing mainly tungsten or an alloy mainly of tungsten while the other ofsaid metal is a metal selected from the group consisting of molybdenum,rhodium, silver, palladium or an alloy mainly of any one thereof.